Previous experience of ethanol withdrawal increases withdrawal-induced c-fos expression in limbic areas, but not withdrawal-induced anxiety and prevents withdrawal-induced elevations in plasma corticosterone

Dynamic c-Fos changes in mouse brain during acute and protracted withdrawal from chronic intermittent ethanol exposure and relapse drinking

Alcohol dependence promotes neuroadaptations in numerous brain areas, leading to escalated drinking and enhanced relapse vulnerability. We previously developed a mouse model of ethanol dependence and relapse drinking in which repeated cycles of chronic intermittent ethanol (CIE) vapor exposure drive a significant escalation of voluntary ethanol drinking. In the current study, we used this model to evaluate changes in neuronal activity (as indexed by c‐Fos expression) throughout acute and protracted withdrawal from CIE (combined with or without a history of ethanol drinking). We analyzed c‐Fos protein expression in 29 brain regions in mice sacrificed 2, 10, 26, and 74 hours or 7 days after withdrawal from 5 cycles of CIE. Results revealed dynamic time‐ and brain region‐dependent changes in c‐Fos activity over the time course of withdrawal from CIE exposure, as compared with nondependent air‐exposed control mice, beginning with markedly low expression levels upon removal from the ethanol vapor chambers (2 hours), reflecting intoxication. c‐Fos expression was enhanced during acute CIE withdrawal (10 and 26 hours), followed by widespread reductions at the beginning of protracted withdrawal (74 hours) in several brain areas. Persistent reductions in c‐Fos expression were observed during prolonged withdrawal (7 days) in prelimbic cortex, nucleus accumbens shell, dorsomedial striatum, paraventricular nucleus of thalamus, and ventral subiculum. A history of ethanol drinking altered acute CIE withdrawal effects and caused widespread reductions in c‐Fos that persisted during extended abstinence even without CIE exposure. These data indicate that ethanol dependence and relapse drinking drive long‐lasting neuroadaptations in several brain regions.

Evidence for incentive salience sensitization as a pathway to alcohol use disorder

The incentive salience sensitization (ISS) theory of addiction holds that addictive behavior stems from the ability of drugs to progressively sensitize the brain circuitry that mediates attribution of incentive salience (IS) to reward-predictive cues and its behavioral manifestations. In this article, we establish the plausibility of ISS as an etiological pathway to alcohol use disorder (AUD). We provide a comprehensive and critical review of evidence for: (1) the ability of alcohol to sensitize the brain circuitry of IS attribution and expression; and (2) attribution of IS to alcohol-predictive cues and its sensitization in humans and non-human animals. We point out gaps in the literature and how these might be addressed. We also highlight how individuals with different alcohol subjective response phenotypes may differ in susceptibility to ISS as a pathway to AUD. Finally, we discuss important implications of this neuropsychological mechanism in AUD for psychological and pharmacological interventions attempting to attenuate alcohol craving and cue reactivity.

Prehabilitation in Alcohol Dependence as a Treatment Model for Sustainable Outcomes. A Narrative Review of Literature on the Risks Associated With Detoxification, From Animal Models to Human Translational Research

In this review paper, we discuss how the overarching concept of prehabilitation is applicable to alcohol dependence. Central to prehabilitation are the concepts of expected harm, risks, and proactive planning to eliminate the harm or cope with the risks. We review the evidence from animal models, psychological experimental studies, as well as pharmacological studies, on the potential risks and harms associated with medically assisted alcohol detoxification and the current treatment paradigm for alcohol dependence. Animal models provide an approximation mostly of the physical aspect of alcohol withdrawal and detoxification process and make predictions about the development of the phenomena in humans. Despite their limitations, these models provide good evidence that withdrawal from chronic ethanol use induces cognitive impairment, which is worsened by repeated bouts of withdrawal and that these impairments are dependent on the duration of alcohol withdrawal. Initial clinical observations with alcohol-dependent patients confirmed increased incidence of seizures. In recent years, accumulating evidence suggests that patients who have had repeated episodes of withdrawal also show changes in their affect, increased craving, as well as significant deterioration of cognitive abilities, when compared to patients with fewer withdrawals. Alcohol dependence is associated with tolerance and withdrawal, with neuroadaptations in γ-Aminobutyric Acid-A Receptor (GABA-A) and glutamatergic N-methyl-D-aspartate (NMDA) receptors playing key roles. It is suggested that dysregulation of the NMDA receptor system underpins alcohol-related memory impairments. Finally, we discuss the Structured Preparation for Alcohol Detoxification (SPADe) as an example of how prehabilitation has been applied in clinical practice. We discuss the importance of partial control over drinking as an interim step toward abstinence and early introduction of lifestyle changes for both the patient and the immediate environment prior to detoxification and while the patient is still drinking.

Sex- and hormone-dependent alterations in alcohol withdrawal-induced anxiety and corticolimbic endocannabinoid signaling

Alcohol dependence is associated with anxiety during withdrawal. The endocannabinoid (ECB) system participates in the neuroendocrine and behavioral response to stress and changes in corticolimbic ECB signaling may contribute to alcohol withdrawal-induced anxiety. Moreover, symptoms of alcohol withdrawal differ between sexes and sexual dimorphism in withdrawal-induced ECB recruitment may be a contributing factor. Herein, we exposed intact male and female rats and ovariectomized (OVX) female rats with or without estradiol (E₂) replacement to 6 weeks of chronic intermittent alcohol vapor and measured anxiety-like behavior, ECB content, and ECB-related mRNA in the basolateral amygdala (BLA) and ventromedial prefrontal cortex (vmPFC). Acute alcohol withdrawal increased anxiety-like behavior, produced widespread disturbances in ECB-related mRNA, and reduced anandamide (AEA) content in the BLA and 2-arachidonoylglycerol (2-AG) content in the vmPFC of male, but not female rats. Similar to males, alcohol-exposed OVX females showed reductions in Napepld mRNA in the BLA, decreased AEA content in the BLA and vmPFC, and reductions in all ECB-related genes measured in the vmPFC. Importantly, E₂ replacement prevented withdrawal-induced alterations in ECB content (but not mRNA) in OVX females, and although alcohol-exposed OVX females failed to exhibit more anxiety compared to their respective control, chronic alcohol exposure abolished the anxiolytic properties of E₂ in OVX rats. These data indicate that ovarian sex hormones (but not E₂ alone) protect against withdrawal-induced alterations in corticolimbic ECB signaling but do not impart resilience to withdrawal-induced anxiety. Thus, the mechanisms implicated in the manifestation of alcohol withdrawal-induced anxiety are most likely sex-specific. This article is part of the Special Issue entitled "A New Dawn in Cannabinoid Neurobiology".

Limbic circuitry activation in ethanol withdrawal is regulated by a chromosome 1 locus

Physiological dependence and associated withdrawal episodes are thought to constitute a motivational force sustaining alcohol use/abuse and contributing to relapse in alcoholics. Although no animal model exactly duplicates alcoholism, models for specific factors, including the withdrawal syndrome, are useful for identifying potential genetic and neural determinants of liability in humans. We previously identified highly significant quantitative trait loci (QTLs) with large effects on predisposition to withdrawal after chronic and acute alcohol exposure in mice and mapped these loci to the same region of chromosome 1 (Alcdp1 and Alcw1, respectively). The present studies utilize a novel Alcdp1/Alcw1 congenic model (in which an interval spanning Alcdp1 and Alcw1 from the C57BL/6J donor strain [build GRCm38 150.3-174.6 Mb] has been introgressed onto a uniform inbred DBA/2J genetic background) known to demonstrate significantly less severe chronic and acute withdrawal compared to appropriate background strain animals. Here, using c-Fos induction as a high-resolution marker of neuronal activation, we report that male Alcdp1/Alcw1 congenic animals demonstrate significantly less alcohol withdrawal-associated neural activation compared to appropriate background strain animals in the prelimbic and cingulate cortices of the prefrontal cortex as well as discrete regions of the extended amygdala (i.e., basolateral) and extended basal ganglia (i.e., dorsolateral striatum, and caudal substantia nigra pars reticulata). These studies are the first to begin to elucidate circuitry by which this confirmed addiction-relevant QTL could influence behavior. This circuitry overlaps limbic circuitry involved in stress, providing additional mechanistic information. Alcdp1/Alcw1 maps to a region syntenic with human chromosome 1q, where multiple studies find significant associations with risk for alcoholism.

Long-Lasting Effects of Chronic Intermittent Alcohol Exposure in Adolescent Mice on Object Recognition and Hippocampal Neuronal Activity

BACKGROUND

Binge drinking is popular and highly prevalent in teenagers. However, the long-term cognitive and neurobiological consequences of such practices are not yet fully understood. In this context, we therefore assessed in mice whether a chronic intermittent alcohol (CIA) exposure in adolescence had long-term consequences on object discrimination and memory performances, emotional behaviors, brain activity, and morphology.

METHODS

C57BL/6JRj mice were treated with either saline or ethanol (EtOH) (2 g/kg/d, i.p., from postnatal days [PND] 30 to PND 44 every other day). The day following the last administration or later in adulthood (PND 71) mice were tested for different behavioral tests (novel object recognition, spontaneous alternation, light-dark box, elevated plus-maze, actimeter test), to assess object recognition, working memory performances, anxiety-like behavior, and locomotor activity. We also investigated neuronal activation of hippocampus, prefrontal and perirhinal cortices, and anatomical changes using immediate-early gene expression and longitudinal brain magnetic resonance imaging.

RESULTS

Our results showed that adolescent mice exposed to CIA present a critical and persistent impairment of short-term object recognition performances. By contrast, spatial working memory was not impaired, nor was anxiety-like behavior. This altered object discrimination was associated with a biphasic change in neuronal activity in the hippocampus but without morphological changes. Indeed, c-Fos expression was specifically increased in the dorsal dentate gyrus (DG) of the hippocampus after the binge exposure, but then became significantly lower in adulthood both in the DG and the CA1 part of the hippocampus compared with adult saline pretreated mice.

CONCLUSIONS

These findings provide evidence for adolescent vulnerability to the effects of intermittent binge EtOH exposure on object discrimination and hippocampal activity with long-lasting consequences.

Effects of acupuncture at Zu-San-Li (ST36) on the activity of the hypothalamic--pituitary--adrenal axis during ethanol withdrawal in rats

The current study investigated the effects of acupuncture at Zu-San-Li (ST36) on the hypothalamic-pituitary-adrenal axis during ethanol withdrawal in rats. Rats were intraperitoneally treated with 3 g/kg/day of ethanol or saline for 28 days. Following 24 hours of ethanol withdrawal, acupuncture was applied at bilateral ST36 points or non-acupoints (tail) for 1 minute. Plasma levels of corticosterone (CORT) and adrenocorticotropic hormone (ACTH) were measured by radioimmunoassay (RIA), and the corticotropin-releasing factor (CRF) protein levels in the paraventricular nucleus of the hypothalamus were also examined by RIA 20 minutes after the acupuncture treatment. RIA showed significantly increased plasma levels of CORT and ACTH in the ethanol-withdrawn rats compared with the saline-treated rats, which were inhibited significantly by the acupuncture at the acupoint ST36 but not at the non-acupoint. Additionally, ethanol withdrawal promoted CRF protein expressions in the paraventricular nucleus of the hypothalamus, which were also blocked by the acupuncture at ST36. These findings suggest that acupuncture at the specific acupoint ST36 can inhibit ethanol withdrawal-induced hyperactivation of hypothalamic-pituitary-adrenal axis, and it may be mediated via the modulation of hypothalamic CRF.

Expression of cFos and brain-derived neurotrophic factor in cortex and hippocampus of ethanol-withdrawn male and female rats

Objective:

To map areas of brain activation (cFos) alongside changes in levels of brain-derived neurotrophic factor (BDNF) to provide insights into neuronal mechanisms contributing to previously observed sex differences in behavioral measures of ethanol withdrawal (EW).

Materials and Methods:

Immunohistochemical analysis of cFos and BDNF levels using protein-specific antibodies and visualization with nickel-enhanced DAB staining in 3 cortical and 4 hippocampal regions was used to assess EW-induced expression of these proteins.

Results:

EW male and female rats showed significantly higher levels of cFos expression compared to controls in the hippocampal regions whereas EW OVX rats showed higher levels compared to controls only at 1 day EW in the dentate gyrus. Males expressed higher basal levels of cFos in the CA1 subfield of the hippocampus and in the motor cortex than either intact or OVX female rats. BDNF immunoreactivity was also significantly higher in EW rats compared to that in controls, varying with sex and brain region at 1 and 3 days EW.

Conclusions:

Sex-and brain region-specific changes in expression of cFos and BDNF occurring during 1 and 3-day EW, suggest that differential activation and expression of neurotrophins may influence the observed sex differences and support the suggestion that EW is a chronic stressor, eliciting sequential neuronal activation and neurotrophin regulation.

Long-term ethanol and corticosterone co-exposure sensitize the hippocampal ca1 region pyramidal cells to insult during ethanol withdrawal in an NMDA GluN2B subunit-dependent manner

BACKGROUND

Chronic ethanol (EtOH) exposure produces neuroadaptations in NMDA receptor function and/or abundance and alterations in hypothalamic-pituitary-adrenal (HPA) axis functioning that contribute to neuronal excitation and neurotoxicity during ethanol withdrawal (EWD). Both EtOH and corticosterone (CORT) promote synthesis of polyamines, which allosterically potentiate NMDA receptor function at the GluN2B subunit. The current studies investigated the effect of 10-day EtOH and CORT co-exposure on toxicity during EWD in rat hippocampal explants and hypothesized that alterations in function and/or density of GluN2B subunits contribute to the toxicity.

METHODS

Organotypic hippocampal slice cultures were exposed to CORT (0.01-1.0 μM) during 10-day EtOH exposure (50 mM) and 1 day of EWD. EtOH-naïve cultures were exposed to CORT for 11 days. Additional cultures were exposed to a membrane impermeable form of CORT (BSA-CORT) with and without 10-day EtOH exposure and EWD. Cytotoxicity (uptake of propidium iodide) was assessed in the pyramidal cell layer of the CA1 region. Western blot analysis was employed to assess the density of GluN2B subunits following EtOH and CORT exposure.

RESULTS

EWD did not produce overt neurotoxicity. However, co-exposure to EtOH/EWD and CORT produced significant neurotoxicity in the CA1 region pyramidal cell layer. Ifenprodil, a GluN2B polyamine site antagonist, significantly reduced toxicity from EtOH and CORT (0.1 μM) co-exposure during EWD. However, Western blots did not reveal differences in GluN2B subunit density among groups. Exposure to BSA-CORT did not produce toxicity, suggesting that membrane-bound CORT receptors did not significantly contribute to the observed toxicity.

CONCLUSIONS

These data suggest that CORT and EtOH co-exposure result in increased function of polyamine-sensitive GluN2B subunits, but this toxicity does not appear dependent on the abundance of hippocampal NMDA GluN2B subunits or membrane-bound CORT receptor function.

Recruitment of medial prefrontal cortex neurons during alcohol withdrawal predicts cognitive impairment and excessive alcohol drinking

Chronic intermittent access to alcohol leads to the escalation of alcohol intake, similar to binge drinking in humans. Converging lines of evidence suggest that impairment of medial prefrontal cortex (mPFC) cognitive function and overactivation of the central nucleus of the amygdala (CeA) are key factors that lead to excessive drinking in dependence. However, the role of the mPFC and CeA in the escalation of alcohol intake in rats with a history of binge drinking without dependence is currently unknown. To address this issue, we examined FBJ murine osteosarcoma viral oncogene homolog (Fos) expression in the mPFC, CeA, hippocampus, and nucleus accumbens and evaluated working memory and anxiety-like behavior in rats given continuous (24 h/d for 7 d/wk) or intermittent (3 d/wk) access to alcohol (20% vol/vol) using a two-bottle choice paradigm. The results showed that abstinence from alcohol in rats with a history of escalation of alcohol intake specifically recruited GABA and corticotropin-releasing factor (CRF) neurons in the mPFC and produced working memory impairments associated with excessive alcohol drinking during acute (24-72 h) but not protracted (16 -68 d) abstinence. Moreover, abstinence from alcohol was associated with a functional disconnection of the mPFC and CeA but not mPFC and nucleus accumbens. These results show that recruitment of a subset of GABA and CRF neurons in the mPFC during withdrawal and disconnection of the PFC-CeA pathway may be critical for impaired executive control over motivated behavior, suggesting that dysregulation of mPFC interneurons may be an early index of neuroadaptation in alcohol dependence.

Blockade of GABA(A) receptors in the paraventricular nucleus of the hypothalamus attenuates voluntary ethanol intake and activates the hypothalamic-pituitary-adrenocortical axis

The paraventricular nucleus (PVN) in the hypothalamus is the main integration site that controls the hypothalamic-pituitary-adrenal (HPA) neuroendocrine stress system. Disruption of this system has been linked with alcoholism, but the specific role of the PVN has not been fully explored. Of particular interest is the ability of γ-aminobutyric acid type A receptors (GABA(A)Rs) in the PVN, to regulate ethanol self-administration behavior, as these receptors appear to play an essential role in mediating the effects of ethanol in the central nervous system and in the regulation of PVN activity. We observed that Long-Evans rats, in the intermittent access to 20% ethanol paradigm, consumed high amounts of ethanol and subsequently developed ethanol dependence. Microinjection of the GABA(A)R antagonist picrotoxin into the PVN, but not to the lateral ventricle of the brain, significantly reduced the intake of ethanol, but not the intake of sucrose. Picrotoxin-induced reduction was mimicked by another GABA(A)R antagonist bicuculline but was attenuated by the GABA(A)R agonist muscimol. Moreover, increased ethanol consumption was associated with lowered blood corticosterone levels, indicating a blunted HPA signaling, which was reversed by intra-PVN injection of picrotoxin, as indicated by the increased Fos immunostaining-positive cells in the PVN and the increased blood corticosterone levels. Taken together, our data provide evidence that in ethanol-dependent rats, the function of GABA(A)Rs in the PVN is upregulated, leading to a dampened HPA system. Moreover, it demonstrates that the GABA(A)R antagonists normalize HPA axis signaling and reduce excessive ethanol drinking. Therefore, drugs targeting GABA(A)Rs may be beneficial for alcoholics.

The relationship between duration of initial alcohol exposure and persistence of molecular tolerance is markedly nonlinear

The neuronal calcium- and voltage-activated BK potassium channel is modulated by ethanol, and plays a role in behavioral tolerance in vertebrates and invertebrates. We examine the influence of temporal parameters of alcohol exposure on the characteristics of BK molecular tolerance in the ventral striatum, an important component of brain reward circuitry. BK channels in striatal neurons of C57BL/6J mice exhibited molecular tolerance whose duration was a function of exposure time. After 6 h exposure to 20 mm (0.09 mg%) ethanol, alcohol sensitivity was suppressed beyond 24 h after withdrawal, while after a 1 or 3 h exposure, sensitivity had significantly recovered after 4 h. This temporally controlled transition to persistent molecular tolerance parallels changes in BK channel isoform profile. After withdrawal from 6 h, but not 3 h alcohol exposure, mRNA levels of the alcohol-insensitive STREX (stress axis-regulated exon) splice variant were increased. Moreover, the biophysical properties of BK channels during withdrawal from 6 h exposure were altered, and match the properties of STREX channels exogenously expressed in HEK 293 cells. Our results suggest a temporally triggered shift in BK isoform identity. Once activated, the transition does not require the continued presence of alcohol. We next determined whether the results obtained using cultured striatal neurons could be observed in acutely dissociated striatal neurons, after alcohol administration in the living mouse. The results were in remarkable agreement with the striatal culture data, showing persistent molecular tolerance after injections producing 6 h of intoxication, but not after injections producing only 3 h of intoxication.

Ethanol modulation of synaptic plasticity

Synaptic plasticity in the most general terms represents the flexibility of neurotransmission in response to neuronal activity. Synaptic plasticity is essential both for the moment-by-moment modulation of neural activity in response to dynamic environmental cues and for long-term learning and memory formation. These temporal characteristics are served by an array of pre- and post-synaptic mechanisms that are frequently modulated by ethanol exposure. This modulation likely makes significant contributions to both alcohol abuse and dependence. In this review, I discuss the modulation of both short-term and long-term synaptic plasticity in the context of specific ethanol-sensitive cellular substrates. A general discussion of the available preclinical, animal-model based neurophysiology literature provides a comparison between results from in vitro and in vivo studies. Finally, in the context of alcohol abuse and dependence, the review proposes potential behavioral contributions by ethanol modulation of plasticity.

Rostroventral caudate putamen involvement in ethanol withdrawal is influenced by a chromosome 4 locus

Physiological dependence and associated withdrawal episodes are thought to constitute a motivational force that sustains alcohol use and abuse and may contribute to relapse in dependent individuals. Although no animal model duplicates alcoholism, models for specific factors, like withdrawal, are useful for identifying potential genetic and neural determinants of liability in humans. Previously, we identified a quantitative trait locus (QTL) and gene (Mpdz, which encodes the multi-PDZ domain protein) on chromosome 4 with a large effect on alcohol withdrawal in mice. Using congenic mice that confirm this QTL and c-Fos expression as a high-resolution marker of neuronal activation, we report that congenic mice show significantly less neuronal activity associated with alcohol withdrawal in the rostroventral caudate putamen (rvCP), but not other parts of the striatum, compared with background strain mice. Moreover, bilateral rvCP lesions significantly increase alcohol withdrawal severity. Using retrograde (fluorogold) and anterograde (Texas Red conjugated dextran amine) tract tracing, we found that ∼25% of c-Fos immunoreactive rvCP neurons project to caudolateral substantia nigra pars reticulata (clSNr), which we previously found is crucially involved in withdrawal following acute and repeated alcohol exposure. Our results expand upon work suggesting that this QTL impacts alcohol withdrawal via basal ganglia circuitry associated with limbic function, and indicate that an rvCP-clSNr projection plays a critical role. Given the growing body of evidence that the syntenic region of human chromosome 9p and human MPDZ gene are associated with alcohol abuse, our results may facilitate research on alcohol dependence and associated withdrawal in clinical populations.

Increased voluntary ethanol consumption and c-Fos expression in selected brain areas induced by fear memory retrieval in ethanol withdrawn rats

Withdrawal from chronic ethanol administration facilitated the formation of contextual fear memory. The effect of fear memory retrieval on subsequent ethanol consumption, by employing a two-bottle free-choice procedure with either water or ethanol (2-8% v/v), was investigated in ethanol withdrawn rats. The effect of fear memory extinction with or without d-cycloserine (DCS, 5mg/kgi.p.) on subsequent ethanol consumption was also evaluated. In addition, we examined c-Fos expression in different brain areas following the fear memory recall. The retrieval of such fear memory induced a significant increase in ethanol consumption in ethanol withdrawn but not in control animals. Regardless of DCS treatment, this increase was attenuated by extinction training. In ethanol withdrawn rats, context-dependent memory retrieval was accompanied by an increased c-Fos expression in the basolateral amygdala, ventrolateral periaqueductal gray, dentate gyrus and dorsomedial periaqueductal gray. Among these brain areas suggested to be implicated in the modulation of motivation and of emotional states, the basolateral amygdala has a crucial role in the emergence of negative affective state during ethanol withdrawal. These data suggest that retrieval of fear memory in ethanol withdrawn rats affected ethanol consumption and that amygdala may be involved in this effect.

The effect of alcohol and nicotine abuse on gene expression in the brain

Alcohol intake at levels posing an acute heath risk is common amongst teenagers. Alcohol abuse is the second most common mental disorder worldwide. The incidence of smoking is decreasing in the Western world but increasing in developing countries and is the leading cause of preventable death worldwide. Considering the longstanding history of alcohol and tobacco consumption in human societies, it might be surprising that the molecular mechanisms underlying alcohol and smoking dependence are still incompletely understood. Effective treatments against the risk of relapse are lacking. Drugs of abuse exert their effect manipulating the dopaminergic mesocorticolimbic system. In this brain region, alcohol has many potential targets including membranes and several ion channels, while other drugs, for example nicotine, act via specific receptors or binding proteins. Repeated consumption of drugs of abuse mediates adaptive changes within this region, resulting in addiction. The high incidence of alcohol and nicotine co-abuse complicates analysis of the molecular basis of the disease. Gene expression profiling is a useful approach to explore novel drug targets in the brain. Several groups have utilised this technology to reveal drug-sensitive pathways in the mesocorticolimbic system of animal models and in human subjects. These studies are the focus of the present review.

Glutamate plasticity in the drunken amygdala: the making of an anxious synapse

Plasticity at glutamatergic synapses is believed to be the cellular correlate of learning and memory. Classic fear conditioning, for example, is dependent upon NMDA-type glutamate receptor activation in the lateral/basolateral amygdala followed by increased synaptic expression of AMPA-type glutamate receptors. This review provides an extensive comparison between the initiation and expression of glutamatergic plasticity during learning/memory and glutamatergic alterations associated with chronic ethanol exposure and withdrawal. The parallels between these neuro-adaptive processes suggest that long-term ethanol exposure might "chemically condition" amygdala-dependent fear/anxiety via the increased function of pre- and post-synaptic glutamate signaling.

Modeling withdrawal syndrome in zebrafish

The zebrafish (Danio rerio) is rapidly becoming a popular model species in behavioral neuroscience research. Zebrafish behavior is robustly affected by environmental and pharmacological manipulations, and can be examined using exploration-based paradigms, paralleled by analysis of endocrine (cortisol) stress responses. Discontinuation of various psychotropic drugs evokes withdrawal in both humans and rodents, characterized by increased anxiety. Sensitivity of zebrafish to drugs of abuse has been recently reported in the literature. Here we examine the effects of ethanol, diazepam, morphine and caffeine withdrawal on zebrafish behavior. Overall, discontinuation of ethanol, diazepam and morphine produced anxiogenic-like behavioral or endocrine responses, demonstrating the utility of zebrafish in translational research of withdrawal syndrome.

Differential activation of limbic circuitry associated with chronic ethanol withdrawal in DBA/2J and C57BL/6J mice

Although no animal model exactly duplicates clinically defined alcoholism, models for specific factors, such as the withdrawal syndrome, are useful for identifying potential neural determinants of liability in humans. The well-documented difference in withdrawal severity following chronic ethanol exposure, between the DBA/2J and C57BL/6J mouse strains, provides an excellent starting point for dissecting the neural circuitry affecting predisposition to physical dependence on ethanol. To induce physical dependence, we used a paradigm in which mice were continuously exposed to ethanol vapor for 72h. Ethanol-exposed and air-exposed (control) mice received daily injections of pyrazole hydrochloride, an alcohol dehydrogenase inhibitor, to stabilize blood ethanol levels. Ethanol-dependent and air-exposed mice were killed 7h after removal from the inhalation chambers. This time point corresponds to the time of peak ethanol withdrawal severity. The brains were processed to assess neural activation associated with ethanol withdrawal indexed by c-Fos immunostaining. Ethanol-withdrawn DBA/2J mice showed significantly (P<.05) greater neural activation than ethanol-withdrawn C57BL/6J mice in the dentate gyrus, hippocampus CA3, lateral septum, basolateral and central nuclei of the amygdala, and prelimbic cortex. Taken together with results using an acute model, our data suggest that progression from acute ethanol withdrawal to the more severe withdrawal associated with physical dependence following chronic ethanol exposure involves recruitment of neurons in the hippocampal formation, amygdala, and prelimbic cortex. To our knowledge, these are the first studies to use c-Fos to identify the brain regions and neurocircuitry that distinguish between chronic and acute ethanol withdrawal severity using informative animal models.

The role of GABA(A) receptors in the acute and chronic effects of ethanol: a decade of progress

The past decade has brought many advances in our understanding of GABA(A) receptor-mediated ethanol action in the central nervous system. We now know that specific GABA(A) receptor subtypes are sensitive to ethanol at doses attained during social drinking while other subtypes respond to ethanol at doses attained by severe intoxication. Furthermore, ethanol increases GABAergic neurotransmission through indirect effects, including the elevation of endogenous GABAergic neuroactive steroids, presynaptic release of GABA, and dephosphorylation of GABA(A) receptors promoting increases in GABA sensitivity. Ethanol's effects on intracellular signaling also influence GABAergic transmission in multiple ways that vary across brain regions and cell types. The effects of chronic ethanol administration are influenced by adaptations in GABA(A) receptor function, expression, trafficking, and subcellular localization that contribute to ethanol tolerance, dependence, and withdrawal hyperexcitability. Adolescents exhibit altered sensitivity to ethanol actions, the tendency for higher drinking and longer lasting GABAergic adaptations to chronic ethanol administration. The elucidation of the mechanisms that underlie adaptations to ethanol exposure are leading to a better understanding of the regulation of inhibitory transmission and new targets for therapies to support recovery from ethanol withdrawal and alcoholism.

Chronic ethanol and withdrawal effects on kainate receptor-mediated excitatory neurotransmission in the rat basolateral amygdala

Withdrawal (WD) anxiety is a significant factor contributing to continued alcohol abuse in alcoholics. This anxiety is extensive, long-lasting, and develops well after the obvious physical symptoms of acute WD. The neurobiological mechanisms underlying this prolonged WD-induced anxiety are not well understood. The basolateral amygdala (BLA) is a major emotional center in the brain and regulates the expression of anxiety. New evidence suggests that increased glutamatergic function in the BLA may contribute to WD-related anxiety following chronic ethanol exposure. Recent evidence also suggests that kainate-type ionotropic glutamate receptors are inhibited by intoxicating concentrations of acute ethanol. This acute sensitivity suggests potential (KA-R) contributions by these receptors to the increased glutamatergic function seen during chronic exposure. Therefore, we examined the effect of chronic intermittent ethanol (CIE) and WD on KA-R-mediated synaptic transmission in the BLA of Sprague-Dawley rats. Our study showed that CIE, but not WD, increased synaptic responses mediated by KA-Rs. Interestingly, both CIE and WD occluded KA-R-mediated synaptic plasticity. Finally, we found that BLA field excitatory postsynaptic potential responses were increased during CIE and WD via a mechanism that is independent of glutamate release from presynaptic terminals. Taken together, these data suggest that KA-Rs might contribute to postsynaptic increases in glutamatergic synaptic transmission during CIE and that the mechanisms responsible for the expression of KA-R-dependent synaptic plasticity might be engaged by chronic ethanol exposure and WD.

Review. Cognitive and emotional consequences of binge drinking: role of amygdala and prefrontal cortex

Binge drinking is an increasingly recognized problem within the UK. We have studied the relationship of binge drinking to cognitive and emotional functioning in young adults, and have found evidence for increased impulsivity, impairments in spatial working memory and impaired emotional learning. Since in human studies it is difficult to understand whether such behavioural changes pre-date or are a consequence of binge drinking, we have also studied parallel behaviours in a rodent model, in which rats are exposed to intermittent episodes of alcohol consumption and withdrawal. In this model, and in parallel with our findings in human binge drinkers, and alcoholic patients who have undergone multiple episodes of detoxification, we have found evidence for impairments in aversive conditioning as well as increased impulsivity. These behavioural changes are accompanied by facilitated excitatory neurotransmission and reduced plasticity (long-term potentiation (LTP)) in amygdala and hippocampus. The impaired LTP is accompanied by both impaired associative learning and inappropriate generalization of previously learned associations to irrelevant stimuli. We propose that repeated episodes of withdrawal from alcohol induce aberrant neuronal plasticity that results in altered cognitive and emotional competences.

Involvement of the limbic basal ganglia in ethanol withdrawal convulsivity in mice is influenced by a chromosome 4 locus

Physiological dependence and associated withdrawal episodes are thought to constitute a motivational force that sustains ethanol (alcohol) use/abuse and may contribute to relapse in alcoholics. Although no animal model duplicates alcoholism, models for specific factors, like the withdrawal syndrome, are useful for identifying potential genetic and neural determinants of liability in humans. We generated congenic mice that confirm a quantitative trait locus (QTL) on chromosome 4 with a large effect on predisposition to alcohol withdrawal. Using c-Fos expression as a high-resolution marker of neuronal activation, congenic mice demonstrated significantly less neuronal activity associated with ethanol withdrawal than background strain mice in the substantia nigra pars reticulata (SNr), subthalamic nucleus (STN), rostromedial lateral globus pallidus, and ventral pallidum. Notably, neuronal activation in subregions of the basal ganglia associated with limbic function was more intense than in subregions associated with sensorimotor function. Bilateral lesions of caudolateral SNr attenuated withdrawal severity after acute and repeated ethanol exposures, whereas rostrolateral SNr and STN lesions did not reduce ethanol withdrawal severity. Caudolateral SNr lesions did not affect pentylenetetrazol-enhanced convulsions. Our results suggest that this QTL impacts ethanol withdrawal via basal ganglia circuitry associated with limbic function and that the caudolateral SNr plays a critical role. These are the first analyses to elucidate circuitry by which a confirmed addiction-relevant QTL influences behavior. This mouse QTL is syntenic with human chromosome 9p. Given the growing body of evidence that a gene(s) on chromosome 9p influences alcoholism, our results can facilitate human research on alcohol dependence and withdrawal.

Functional internal complexity of amygdala: focus on gene activity mapping after behavioral training and drugs of abuse

The amygdala is a heterogeneous brain structure implicated in processing of emotions and storing the emotional aspects of memories. Gene activity markers such as c-Fos have been shown to reflect both neuronal activation and neuronal plasticity. Herein, we analyze the expression patterns of gene activity markers in the amygdala in response to either behavioral training or treatment with drugs of abuse and then we confront the results with data on other approaches to internal complexity of the amygdala. c-Fos has been the most often studied in the amygdala, showing specific expression patterns in response to various treatments, most probably reflecting functional specializations among amygdala subdivisions. In the basolateral amygdala, c-Fos expression appears to be consistent with the proposed role of this nucleus in a plasticity of the current stimulus-value associations. Within the medial part of the central amygdala, c-Fos correlates with acquisition of alimentary/gustatory behaviors. On the other hand, in the lateral subdivision of the central amygdala, c-Fos expression relates to attention and vigilance. In the medial amygdala, c-Fos appears to be evoked by emotional novelty of the experimental situation. The data on the other major subdivisions of the amygdala are scarce. In conclusion, the studies on the gene activity markers, confronted with other approaches involving neuroanatomy, physiology, and the lesion method, have revealed novel aspects of the amygdala, especially pointing to functional heterogeneity of this brain region that does not fit very well into contemporarily active debate on serial versus parallel information processing within the amygdala.

The amygdala regulates the antianxiety sensitization effect of flumazenil during repeated chronic ethanol or repeated stress

BACKGROUND

The benzodiazepine receptor antagonist flumazenil reduces anxiety-like behavior and sensitization of anxiety-like behavior in various models of ethanol withdrawal in rodents. The mechanism and brain region(s) that account for this action of flumazenil remain unknown. This investigation explored the potential role of several brain regions (amygdala, raphe, inferior colliculus, nucleus accumbens, and paraventricular hypothalamus) for these actions of flumazenil.

METHODS

Rats were surgically implanted with guide cannulae directed over the brain region of interest and then treated with an ethanol diet for three 7-day dietary cycles (5 days on ethanol diet followed by 2 days on control diet). At approximately 4 hours, flumazenil was administered intracranially into each of the first 2 withdrawals. Examinations of anxiety-like behavior followed 1 week later during a third withdrawal. In other animals, restraint stress sessions or intra-amygdala DMCM (methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate) injections, preceded by intraperitoneal flumazenil injections, were substituted for the first 2 ethanol treatment cycles to assess the potential anxiety-sensitizing action of stress or a benzodiazepine receptor inverse agonist, respectively.

RESULTS

Flumazenil treatment of the amygdala during the first 2 withdrawals blocked the development of sensitized anxiety seen during a third withdrawal. Similar actions of flumazenil were found when stress sessions substituted for the first 2 cycles of ethanol exposure and withdrawal. Amygdala treatment with DMCM magnified the anxiety response to the single subthreshold chronic ethanol treatment, and prophylactic flumazenil blocked this effect.

CONCLUSIONS

Intra-amygdala flumazenil inhibits the development of anxiety sensitized by repeated ethanol withdrawal, stress/ethanol withdrawal, or DMCM/ethanol withdrawal. These actions suggest that site-specific and persistent effects of flumazenil on gamma-aminobutyric acid-modulatory processes in this brain region are relevant to sensitized behavioral effects seen in alcoholism.

Brainstem areas activated by diazepam withdrawal as measured by Fos-protein immunoreactivity in rats

In the 1970s, chronic treatment with benzodiazepines was supposed not to cause dependence. However, by the end of the decade several reports showed that the interruption of a prolonged treatment with diazepam leads to a withdrawal syndrome characterized, among other symptoms, by an exaggerated level of anxiety. In laboratory animals, signs that oscillate from irritability to extreme fear-like behaviors and convulsions have also been reported. In recent years many studies have attempted to disclose the neural substrates responsible for the benzodiazepines withdrawal. However, they have focused on telencephalic structures such as the prefrontal cortex, nucleus accumbens and amygdala. In this study, we examined the Fos immunoreactivity in brain structures known to be implicated in the neural substrates of aversion in rats under spontaneous diazepam-withdrawal. We found that the same group of structures that originally modulate the defensive responses evoked by fear stimuli, including the dorso-medial hypothalamus, the superior and inferior colliculus and the dorsal periaqueductal gray, were most labeled following diazepam withdrawal. It is suggested that an enhanced neural activation of neural substrates of fear in the midbrain tectum may underlie the aversive state elicited in diazepam-withdrawn rats.

Baclofen blocks expression and sensitization of anxiety-like behavior in an animal model of repeated stress and ethanol withdrawal

BACKGROUND

Repeated exposures to forced ethanol diets (EDs) or restraint stress sensitize anxiety-like behavior during a future ethanol withdrawal. The present investigation assessed whether pretreatment of rats with agents targeting receptor systems thought to be important in treating relapse in alcoholic patients would prevent sensitization of anxiety-like behavior.

METHODS

Groups of rats were exposed to either (1) three 5-day cycles of ED with 2 days of withdrawal between cycles, (2) continuous ED, or (3) 5 days of ED in a single cycle preceded by 2 episodes of restraint stress 6 days apart. Drugs [baclofen, acamprosate, naloxone, lamotrigine, ifenprodil, dizocilpine (MK-801), CGS19755, diazepam, flumazenil, or 6-methyl-2-(phenylethynyl)pyridine] were given prophylactically during the first and second withdrawal periods only or, in separate baclofen experiments, acutely during the third withdrawal or during withdrawal from continuous ED. Baclofen administration preceded each stress session in the stress-withdrawal protocols. Anxiety-like behavior was assessed in the social interaction (SI) test 5 hours after the ethanol was removed or after 3 days of abstinence.

RESULTS

Baclofen (1.25, 2.5, and 5 mg/kg), flumazenil (5 mg/kg), and diazepam (1 mg/kg) blocked the reduction in SI induced by ethanol withdrawal. Among the drugs that alter glutamate function, only acamprosate (300 mg/kg) was effective. In the stress protocols, baclofen (5 mg/kg) given before each of the 2 restraint stress sessions before ethanol exposure or before stress during abstinence also attenuated SI deficits.

CONCLUSIONS

These findings suggest that GABAB and GABAA, but not glutamate or opioid mechanisms, are involved in adaptive changes associated with anxiety-like behavior induced by these repeated ethanol-withdrawal and stress-withdrawal paradigms. The lack of action of agents attenuating different aspects of glutamate function suggests that acamprosate's action is related to some other, as yet undetermined, mechanism.

Repeated withdrawal from ethanol spares contextual fear conditioning and spatial learning but impairs negative patterning and induces over-responding: evidence for effect on frontal cortical but not hippocampal function?

Repeated exposure of rats to withdrawal from chronic ethanol reduces hippocampal long-term potentiation and gives rise to epileptiform-like activity in hippocampus. We investigated whether such withdrawal experience also affects learning in tasks thought to be sensitive to hippocampal damage. Rats fed an ethanol-containing diet for 24 days with two intermediate 3-day withdrawal episodes, resulting in intakes of 13-14 g/kg ethanol per day, showed impaired negative patterning discrimination compared with controls and animals that had continuous 24-day ethanol treatment, but did not differ from these animals in the degree of contextual freezing 24 h after training or in spatial learning in the Barnes maze. Repeatedly withdrawn animals also showed increased numbers of responses in the period immediately before reinforcement became available in an operant task employing a fixed-interval schedule although overall temporal organization of responding was unimpaired. Thus, in our model of repeated withdrawal from ethanol, previously observed changes in hippocampal function did not manifest at the behavioural level in the tests employed. The deficit seen after repeated withdrawal in the negative patterning discrimination and over-responding in the fixed-interval paradigm might be related to the changes in the functioning of the cortex after withdrawal.